The invention relates to a fuel injection system for an internal combustion engine.
Fuel injection systems for internal combustion engines, particularly diesel engines, are becoming increasingly wide-spread. The fuel injection systems contain a high-pressure pump for delivering the fuel from a fuel reservoir, a number of fuel injectors for injecting the fuel into the combustion space of the internal combustion engine, and a high-pressure fuel line. The high-pressure fuel line connects the high-pressure pump with the fuel injectors and contains a high-pressure reservoir for holding the fuel to be injected which is delivered by the high-pressure pump at a high pressure (common rail systems). An important advantage of such fuel injection systems is that, with respect to the injection start, the injection duration and the mass flow rate of the injected fuel per time unit, the injection operation can be very precisely adapted to the respective rotational speed condition and load condition of the internal combustion engine. In addition to the high-pressure fuel line which delivers the fuel from the high-pressure pump to the fuel injectors and holds the fuel at a high pressure, in the case of these fuel injection systems, a fuel return flow line as well as a leakage line for returning the occurring leakage quantities, which occur at the fuel injectors or because of leakiness of the sealing points, are provided. The provision of these additional fuel lines is already connected with high expenditures and, particularly in the case of large-volume diesel engines, significant vibration-related problems in connection to the mounting of the lines at the engine.
It is an object of the present invention to provide a fuel injection system of the above-mentioned type which is improved with respect to the guidance of these fuel lines.
In accordance with one aspect of the invention, a fuel injection system for an internal combustion engine includes a high-pressure pump for delivering the fuel from a fuel reservoir, a number of fuel injectors for injecting the fuel into the combustion space of the internal combustion engine and a high-pressure fuel line. The high-pressure fuel line connects the high-pressure pump with the fuel injectors and contains a high-pressure reservoir for holding the fuel to be injected which is delivered at a high pressure by the high-pressure pump. Furthermore, a fuel return flow line for returning non-injected fuel and a leakage line are provided. According to the invention, the high-pressure fuel line, the fuel return flow line and the leakage line are combined in a common fuel line with respective flow cross-sections for each of the lines, which flow cross-sections are separated by walls.
A significant advantage of the fuel system according to the invention is the fact that fastening parts, sealing and connecting elements required for the separate mounting of the fuel return flow line and of the leakage line are eliminated. This avoids the risk of a functional failure of such elements, and no difficulties occur with respect to vibration problems of such lines.
In a preferred embodiment of the fuel injection system according to the invention, the common fuel line is formed by three coaxially arranged, mutually surrounding line pipes. The interior pipe is the high-pressure fuel line, and it is surrounded by inner and outer jacket pipes which each enclose a flow cross-section and form the fuel return line and the leakage line. This results in the advantage that the high-pressure fuel line which, because of the required high-pressure stability, has a very massive construction, forms a stable support for the surrounding jacket pipes, thereby neutralizing the vibration problems.
According to a preferred embodiment, the jacket pipes surrounding the high-pressure fuel line are provided with ducts on their interior surface, which ducts extend in the longitudinal direction and form the flow cross-sections of the fuel return line and of the leakage line respectively.
In this case, the jacket pipes surrounding the high-pressure fuel line preferably have webs on their inner surface between the ducts forming the flow cross-sections of the fuel return line and the leakage line respectively. The webs rest against the outer circumference of the respective inner line surrounded by the respective jacket pipe.
According to a preferred embodiment of the invention, the inner jacket pipe surrounding the high-pressure fuel line forms the leakage line, and the outer jacket pipe surrounding the inner jacket pipe forms the fuel return line.
According to a preferred embodiment of the invention, the fuel injectors of the injection system each have a common high-pressure connection provided with a high-pressure duct mouth for the connection of the high-pressure fuel line, a leakage duct mouth for the connection of the leakage line, and a return flow duct mouth for the connection of the fuel return flow line. This results in the advantage that the high-pressure fuel line, the leakage line and the fuel return flow line are all connected to a joint connection directly on the fuel injector, so that no ducts for removing return flow or leakage amounts from the fuel injector have to be provided in the cylinder head of the internal combustion engine.
A particularly preferred embodiment of the invention provides that the joint high-pressure connection has on its face a centrally arranged high-pressure duct mouth for the connection of the high-pressure fuel line and has on its circumference, spaced away from one another in the axial direction, the leakage duct mouth for the connection of the leakage line and the return flow duct mouth for the connection of the return flow line. The individual mouths each are sealed off by sealing elements and separated from the other mouths.
According to a further development, the sealing element of the high-pressure duct mouth is formed from a conical seal interacting with a sealing cone constructed at the end of the high-pressure fuel line. The sealing elements sealing off the leakage duct mouth and the return flow duct mouth are formed from O-rings which interact with the inner circumferential surface of a screw-over sleeve having flow cross-sections which are assigned to the leakage line and the fuel return flow line and are spaced away from one another in the axial direction.
In the following, an embodiment of the invention will be explained by means of the drawing.